1. Field of the Invention
This invention relates to a photoelectric transducing element for an image or visual information processing photoelectric converter to be adopted in facsimiles, character reading devices, and others.
2. Description of Prior Arts
Photoelectric transducers which have heretofore been used generally and are composed of a long array of one-dimensional photo-diodes formed on a crystalline silicon substrate accompany various disadvantages such that, due to restriction to a practical size of a single crystal of silicon to be the substrate and its processing technique, the length of the light receiving region in the photodiode is restricted, and its yielding rate is also low. Consequently, when an image original to be read has a width of 210 mm (corresponding to A-4 size), it has generally been the practice to focus the image original on the light receiving region of a photo-sensor array in a reduced scale by use of a lens system for the necessary reading. Such method of using the optical lens system not only makes it difficult to reduce the size of the photoelectric converter, but also necessitates a large quantity of light to obtain sufficient photo-signal current because of difficulty in allotting a large area for individual light receiving regions. As the result of this, the photoelectric transducer of this type is, at the present stage, used only for those purposes where the image original reading may be done at a slow pace, or where high image resolution is not required.
On the other hand, elongation in the photosensor array and enlargement in the area of the individual light receiving regions become feasible with the photoelectric transducing element fabricated by forming a photoconductive layer through lamination, on a predetermined substrate, of a thin or thick film which is coated by use of a film forming method using a vaccum deposition device employing the glow discharge method, the sputtering method, the ion-plating method, the vaccum evaporation method, etc., or a method of applying the photoconductive material in mixture with a binding resin.
In such photoelectric transducing element, however, there still remains room for improvement, such that the S/N ratio (photo-current/dark current) is small due to the dark current being relatively large, hence sufficient electrical signal cannot be taken out with respect to the light signal in a region where the light quantity is very small, the resolution is not so high due to cross-talk of signal current among the light receiving sections, and so forth. It is therefore necessary in this elongatable photoelectric transducing element to attempt an increase in the dark resistance of the photoconductive layer, remodelling of the structure of the element, decrease in the dark current, and improvement in the resolution.